#include<stdio.h>
int main()
{
	int h1,h2,m1,m2;
	scanf("%02d%02d %02d%02d",&h1,&m1,&h2,&m2);
	int pass_time = (h2*60+m2)-(h1*60+m1);
	int h=pass_time/60;
	int m=pass_time%60;
	printf("%02d:%02d",h,m);
	return 0;
}
